Cameron Francis’ Exchange Rate gimmick allows you to make an eye popping change between a coin and a folded bill.
You borrow a coin from your spectator. He signs one side, you sign the other. You then offer to blow their mind. and if you can’t, you say, you’ll give them the bill in your pocket (can be any currency)!
Holding their signed coin at your very fingertips (sleeves rolled up), you give one tiny shake and you are now holding the bill! No cover and almost NO sleight of hand.